The invention relates to a method and an arrangement for controlling a plurality of spray tools in a coating line by means of a coating control comprising a centralized control with stored program capability which releases setting magnitudes determining the paint throughput of each spray tool to actuators for the spray tools which, during coating, are moved by drives along paths whose beginning and end depends on signals from the control with stored program capability, with vehicles or parts thereof being moved through the coating line.
A method of the type described above is known from GB A-1 556 013. In a coating station, the known arrangement comprises a vertically movable spray tool for each side and a horizontally movable spray tool for the top side of automobile bodies. Each spray tool is connected to its own comparator control in which six linear movement paths of different lengths are stored for the associated spray tool by their beginning and end points. The control with stored program capability, which is connected to the comparator controls of the spray tools in a star-shaped manner, respectively selects one of these previously stored linear movement paths via a corresponding signal which is decoded in the comparator control. Then, the comparator control compares the signals generated by sensors with the beginning and end points of the movement path selected by the control with stored program capability and respectively releases or blocks the spray tools when the beginning and end points are reached.
Also known is a numerical control for the synchronous movement of machine drives, comprising a centralized computer which, via a parallel main computer bus, is connected to secondary computers respectively provided by a motor control and to a secondary computer control connected to each secondary computer via a second bus. The relatively slow centralized computer calculates interpolation points from stored command data. Sets of interpolation points are respectively transmitted to the secondary computers from the centralized computer. The secondary computers extrapolate the received interpolation data by iteration and generate motor drive signals. The secondary computer control synchronizes the operation and the temporal operating steps of the main computer and of the secondary computers (U.S. Pat. No. 4,262,336).
Finally, a method and an arrangement for determining an at least partially curved movement path of a tool are known by means of which the intermediate points disposed between path support points are determined by way of interpolation. The curved path segments disposed in-between two path support points are first approximated by parallel arcs which are then approximated by a progression by means of Linewinter polation (DE-A-29 45 660).
In automobile bodies, many parts, e. g., the outer sides of the roof, the doors, the hood and the tail, have uniform part geometries. These parts are coated with automatic coating machines, particularly by way of electrostatic spraying. The automatic coating machines have a plurality of spray tools past which the automobile bodies are moved. Frequently, drive and control devices having several axes are employed to arrange the spray tools at distances and angles that are suitable for coating. The spray tools are moved along predetermined paths which depend on the shape and speed of the parts to be coated.
For surface coating, pneumatic or electrostatic coating processes may be used. In the pneumatic spraying processes, the paint material is atomized in spray guns. In electrostatic spraying processes, an electrostatic field with a high direct voltage is generated between the spray tool and the object to be coated.
During the movement of the automobile body in the coating station, spray tools for the top surfaces and the side surfaces of the bodies are usually in operation simultaneously. The top surfaces and the side surfaces differ in their geometry. Additionally, the top and the side surfaces have different slopes with respect to the horizontal or vertical. Therefore, in order to properly coat the top and side surfaces, the spray tools must be moved at different speeds and be guided along different paths. Other parameters, e.g., paint consumption per time unit, may also vary from one spray tool to another.
For cost-efficiency reasons, automatic coating machines are used that have a plurality of spray tools, all or most of which are in operation at the same time. The spray tools must be positioned at distances and angle positions that are as optimal as possible with respect to the surface part that is to be coated in order to accomplish a uniform paint application. Therefore, it is necessary to position or move at least some of the spray tools independently of one another in terms of their positions and angles in space. For example, the spray tools are oriented perpendicularly onto the respective surface to be coated at uniform distances.
The controls for the spray tools or their drives comprise data for coating patterns which are allocated to surfaces of different shapes. These data relate to the settings of the spray tools and of the paths to be traversed by these tools during the relative movements between the spray tools and the surfaces to be coated. The programming of the controls takes place, for example, in situ or in a separate coating station with the aid of the Teach-In method. Off-line programming is also possible, at least for obtaining coarse path data which can then be corrected, for example, by way of the Teach-In method.
It is now the object of the invention to provide a method and an arrangement for controlling a plurality of spray tools for the surface coating of vehicles or parts thereof, wherein the expenditure for the control is low in spite of the simultaneous operation of several spray tools and precise positioning of the spray tools during the coating process.